This invention relates in general to a method of coating an optical fiber, and in particular to such a method that is carried out immediately after the fiber is drawn and that results in maintaining the mechanical strength of the optical fiber after the fiber has been drawn.
Typical tensile strengths observed for silicon optical fibers at the time the fibers are drawn are on the order of 1 million p.s.i. In certain optical communications, it is necessary to employ optical fibers having lengths above 1 kilometer. The problem in the art when using such long lengths of optical fibers has been the fiber's lack of adequate mechanical strength. That is, the tensile strength of long lengths of commercially available optical fibers is in the range of 15,000 to 20,000 p.s.i. A mechanical strength above 200,000 p.s.i., however, is needed for optical fibers when used as optical waveguides in certain specialized applications, as for example, in rapid payout communication systems employing long lengths of fiber.
The reason that long lengths of fibers have not been prepared with sufficient mechanical strength has been due to the presence of submicron surface flaws caused either by light mechanical abrasion during and after the usual fiber drawing operation and/or by chemical attack by atmospheric contaminants such as moisture. Attempts to solve these problems have been made by applying organic coatings to these fibers after the fibers have been drawn. However, these organic coatings have not been impervious to moisture or hydroxyl ion diffusion. This has led to the reduced strength of organic coated fibers during periods of use or storage.